Limiting the acoustic dispersion of exhaust lines, in particular exhaust line mufflers, is an important aspect of vehicle passenger comfort, as well as the comfort of persons in the environment of said vehicle. This acoustic dispersion primarily comes from two sources: dispersion due to gas excitation and dispersion due to structural excitation.
For exhaust components with a single-layer main casing, one of the methods traditionally used to reduce acoustic dispersion is to increase the rigidity of the main casing, which attenuates the structural excitation. Stiffening is obtained by creating ribs or bosses in the main casing. Another possibility consists of rigidly fastening a sheet on the main casing, thereby creating a local overthickness.
Furthermore, due to the thickness of the main casing, the acoustic dispersion due to gas excitation is greatly attenuated.
Equipment manufacturers in the automotive industry are always concerned with reducing the weight of components on board the vehicle. Consequently, it is desirable to reduce the thickness of the main casing. This has negative effects with respect to acoustic dispersion. Indeed, it causes strong resonances to emerge on the thin sheet. This phenomenon is in particular due to the offset of the resonance frequencies toward the low frequencies. Due to the reduced thickness, the dispersion due to gas excitation is greater, this dispersion being attenuated less through the main casing. Stiffening the main casing alone does not yield satisfactory results.